The invention relates, in general, to a device for aligning sheets which are individually supplied to a collecting tray in which they are stacked one above the other and, in particular, to a sheet-aligning device for use with a collecting tray which comprises a support surface and a lateral limiting wall arranged parallely with the direction of entrance of the sheets as well as an abutment associated with the front end side of the sheets, such device including a drivable wheel which is arranged at the free end of a pivotable arm and rests on the incoming sheet and which aligns such sheet both at the lateral limiting wall and at the front abutment.
It is known (see, for example DE-31 07 768, C2) for individually supplied sheets to be aligned with respect to a front abutment and a lateral limiting wall of a collecting tray by a roller positioned obliquely to the direction of sheet transport. It is also known (see, for example U.S. Pat. No. 4,718,657) for the surface of the sheet stack to be sensed and kept at a predetermined level by means of a rotatable and pivotable aligning roller which serves to stack the sheets in a staggered arrangement. In both of these known devices, the aligning roller constantly subjects the uppermost sheet to the same pressure force, whereby, in particular, thin sheets of only slight inherent stiffness may become compressed so that the plane position of the sheets deposited cannot be ensured. If sheets collected in stacks are to be further processed, for example stapled in sets, the sheets must be sufficiently plane to allow them to be properly stapled.